Yes, I had noticed that. The large majority of the 28 minutes or so that the film lasts is about the 1959 June Sprints small production race, but, as you say, if you keep a sharp eye every now and then a scene from the 1959 RA 500 sneaks in. A bit jarring, if you are paying attention, but I daresay most people who view it will not catch those splicing/editing errors.
Tom